1. Field of the Invention
This invention relates to the field of analysis of biological samples, both solids and liquids, e. g., urinalysis, and, in particular, to apparatus and method for conducting analysis of biological samples without the need for reagents. This invention also relates to detection of adulteration of samples of biological fluid to protect the integrity of analysis results.
2. Discussion of the Art
Determining the concentration of an analyte or a parameter of physical condition in a biological sample has been an important area in the field of diagnostics. Analytes that have diagnostic value includes nutrients, metabolites, enzymes, immunity entities, hormones, and pathogens. The physical characteristics of a biological sample, such as temperature, optical properties, density, and hardness, are also of interest because of their capability of providing indications for diagnostic purposes. Most determination methods use signal-enhancing agents.
Urinalysis involves measuring critical components in a sample of urine to determine the condition of the body with respect to diseases and other substances, e. g., drugs. Urine contains a wide variety of substances. In current urinalysis systems, such as those provided by Bayer and Boehringer Mannheim, the analytes measured include glucose, bilirubin, ketones (80% 3-hydroxybutyrate, 17% acetoacetic acid, 3% acetone), blood (or hemoglobin), protein, urobilinogen, nitrites, and leukocytes. Specific gravity (or refractive index) and pH are also measured. In some cases, measurement of creatinine is suggested, but is not provided by Bayer""s or Boehringer Mannheim""s urinalysis systems. All of these analytes represent breakdown products of metabolism from various organ systems. The pattern of excretion is indicative of various disease states. The history and utility of urinalysis is discussed in Voswinckel, Peter, xe2x80x9cA marvel of colors and ingredients. The story of urine test stripsxe2x80x9d, Kidney International, Vol. 46, Suppl. 47 (1994), pp. S-3-S-7, and Free, Alfred H. and Free, Helen M., xe2x80x9cUrinalysis: Its Proper Role in the Physician""s Officexe2x80x9d, Office Practice of Laboratory Medicine, Clinics in Laboratory Medicinexe2x80x94Vol. 6, No. 2, June 1986, both of which are incorporated herein by reference.
Urinalysis testing is also used as a means to determine which samples of urine need to be examined by microscopy, which is such an expensive and time-consuming procedure that it cannot be performed on all urine samples with current methods. Microscopic examination of urine sediment can confirm the presence of bacterial infection, or white cells, indicating infection or kidney damage, among other indications.
The majority of urinalysis testing is accomplished by means of dip and read strip technology supplied by Bayer and Boehringer Mannheim. Strip technology is well understood and suffers from a number of limitations. Readings must be properly timed to obtain accurate results. Controls must be employed. Urine samples must be well mixed and at room temperature. Strips are sensitive to light and humidity, and must be stored and handled properly. Quantitative results are difficult to obtain. Interfering substances can cause incorrect readings.
Abuse of drugs and other substances is recognized as a significant problem in the United States, and is now being recognized in other parts of the world. As a result, more people are being tested in routine drug screening programs than ever before. In the United States, about 10% of the population is estimated to abuse drugs or alcohol, and about 70% of those are employed. Business and government organizations in the United States will spend about $725,000,000 in 1998 to test selected populations to determine whether their performance may be impaired by abuse of depressants, hallucinogens, hypnotics/sedatives, or stimulants. In most cases, the sample tested is urine. Consequences of failing a routine drug screen can be severe, e. g., loss of employment or loss of freedom if testing is performed for the criminal justice system, and these consequences have led to the development of an industry designed to xe2x80x9cbeatxe2x80x9d a drug test. Drug testing can be xe2x80x9cbeatenxe2x80x9d by simply diluting the sample with water, apple juice, or similar materials. Drug testing can also be xe2x80x9cbeatenxe2x80x9d by attacking the macromolecules and indicators used in the testing systems with materials such as acids, bases, nitrites, and glutaraldehyde, among others.
While estimates of the extent of adulteration are difficult to obtain and some evidence suggests that they vary with the populations tested, estimates of adulteration range as high as 30% of urine samples submitted for testing. The drug of abuse assay system using Enzyme Multiplied Immunoassay Technique (EMIT) is a major high-speed screening tool for drugs of abuse, but it is also among the most sensitive systems to failures caused by sample adulteration. Systems based on fluorescence polarization immunoassay (FPIA) are more robust, but are not immune from failures caused by adulterated samples.
To achieve the social purpose of deterring drug abuse by testing of urine, it is essential to assure the integrity of the samples of urine. Sample integrity can be assured by xe2x80x9cobservedxe2x80x9d collection. However, such a stringent method is applicable only in special situations, and is costly. Legal considerations require a thoroughly documented chain of custody for each sample. A system configuration that permits a check for sample adulteration and simultaneously sequesters the sample for further testing such as GC/mass spectrometry, or for archiving, may be advantageous. The integrity of a urine sample can also be judged by measuring specific gravity, pH, creatinine level, and temperature of the sample before committing the sample to further tests that employ costly reagents. Low levels of creatinine may indicate dilution of the sample. An abnormally low or high value of pH indicates the addition of acid or base. Altered specific gravity indicates the addition of foreign materials, such as apple juice or salts, that may alter test results. If the temperature of a urine sample is unexpectedly low, it may indicate that a sample was substituted, and if the temperature of a urine sample is unexpectedly high, it may indicate that a sample was substituted or that a chemical reaction took place. By ensuring sample integrity, potentially adulterated samples may be rejected for testing, and unadulterated samples may be recollected more quickly, thereby assuring the accuracy of the test results, and preventing impaired individuals from endangering the safety of the public.
There are several methods for measuring creatinine. The oldest, the Jaffee method, requires temperature control for accurate results. The 3.5-DiNitroBenzoic Acid (DNBA) method (similar to the Jaffee method) has been adapted to strips for a serum assay. Both methods have been commercialized with as many as four enzymes by Kodak. When measured with long wavelength infrared radiation, creatinine provides the second strongest signal in urine. Hence, infrared spectroscopy utilizing multivariate mathematical analysis is able to xe2x80x9cpick-outxe2x80x9d creatinine with a high degree of precision and specificity.
The amount of dissolved solids in urine is typically measured by refractive index measurement (the gold standard) or by specific gravity measurements. Measurements of refractive index and specific gravity in urine are highly correlated, as shown by studies of samples of patients in hospitals.
pH is a measure of acid or base content of the urine sample. Standard laboratory practice makes use of a pH electrodes for accurate pH measurements. Miniature pH electrodes have been demonstrated by Nova Biomedical (Waltham, Mass.) in their instruments and by others. Bayer has a block on a colorimetric strip that measures pH in urine with reasonable accuracy for the normal range of pH in urine (4.6-8.0).
It would be desirable to provide a method and a device for analysis of biological samples and detection of sample adulteration that does not encounter the disadvantages of a system based on roagont containing reagent-containing strips. In a reagentless system, the stability, storage, and shelf life issues of reagents would be of no concern. In a reagentless system, the method could be automated and would not require precise timing by the user. Interfering substances could be detected and incorrect readings could be minimized. Proper controls could be incorporated into the system and could be transparent to the user. Quantitative readings could be performed better, and larger dynamic ranges than can be provided by reagont containing reagent-containing strips could be made available. A reagentless system has the additional advantage that it can be adapted to possible future expansion of adulterants when the features of those adulterants become known. If needed, a reagentless system could also be integrated with a reagent-using system to provide a broader menu, better performance, and higher throughput.
This invention provides an apparatus and method for determining at least one parameter, e. g., concentration, of at least one analyte, e. g., urea, of a biological sample, e. g., urine. A biological sample particularly suitable for the apparatus and method of this invention is urine. In general, spectroscopic measurements can be used to quantify the concentrations of one or more analytes in a biological sample. In order to obtain concentration values of certain analytes, such as hemoglobin and bilirubin, visible light spectroscopy can be used. In order to obtain concentration values of other analytes, such as urea, creatinine, glucose, ketones, and protein, infrared light spectroscopy can be used. The apparatus and method of this invention utilize one or more mathematical techniques to improve the accuracy of measurement of parameters of analytes in a biological sample.
In one aspect, the invention provides a method for determining at least one parameter of at least one analyte of a biological sample involving the use of a mathematical technique to assist in reducing noise in signal detection in spectroscopic measurements. More specifically, this invention provides a method for reducing noise in a determination of concentration of at least one analyte of interest in a biological sample by means of spectroscopic analysis comprising the steps of:
(a) identifying a mathematical function that is substantially similar to a region of a non-smoothed spectrum of the sample over a selected range of the non-smoothed spectrum;
(b) selecting a portion of the region of the non-smoothed spectrum such that noise in the selected portion is substantially random;
(c) determining coefficients of the mathematical function that result in a close fit of the function to the selected portion of the non-smoothed spectrum;
(d) calculating at least one value of the non-smoothed spectrum at at least one wavelength of the non-smoothed spectrum by means of the coefficients and the mathematical function of step (c), wherein said at least one wavelength includes the center of the region of the non-smoothed spectrum;
(e) assigning said at least one calculated value of the non-smoothed spectrum to a wavelength including the center of the selected portion of the region of the non-smoothed spectrum to form at least one point of a smoothed spectrum;
(f) shifting a selected distance in the non-smoothed spectrum and repeating steps (c), (d), and (e) until a desired amount of the smoothed spectrum is formed;
(g) forming a residual spectrum by subtracting each point of the desired amount of the smoothed spectrum at a given wavelength from each point of the non-smoothed spectrum at said given wavelength;
(h) inspecting the residual spectrum to determine if it is random; and
(i) if the residual spectrum is not random, repeating steps (b), (c), (d), (e), (f), (g), and (h) to achieve a smoothing, wherein said residual spectrum is random.
In another aspect, the invention provides a method for determining at least one parameter of at least one analyte of a biological sample involving the use of a mathematical technique to assist in elimination of residual signal associated with interfering compounds by the use of multivariate analysis, such as partial least squares. More specifically, this invention provides a method for determining concentration of at least one analyte of interest in a biological sample of an individual by means of spectroscopic analysis comprising the steps of:
(a) identifying at least one analyte that is a major component of said biological sample, said at least one analyte accounting for significant variations with respect to a plurality of spectra of biological samples from a plurality of donors of said biological samples;
(b) measuring a spectrum for each of the plurality of biological samples from the plurality of donors of the biological samples;
(c) calculating a model spectrum for each of the plurality of biological samples from the plurality of donors of the biological samples by mathematically fitting spectra of the analytes of the at least one identified analyte to each spectrum of each of the biological samples from the plurality of donors of the biological samples;
(d) calculating a residual spectrum for each spectrum of each of the biological samples from the plurality of donors of the biological samples by subtracting each value of the model spectrum from each value of the spectrum of the biological samples from the plurality of donors of the biological samples that corresponds to the model spectrum;
(e) repeating steps (a), (b), (c), and (d) at least one time by introducing at least one additional analyte to the model spectrum until the calculated residual spectra are substantially constant from one biological sample to another biological sample of the plurality of biological samples from the plurality of donors of the biological samples;
(f) determining a set of calibration parameters from the model spectra, said set of calibration parameters accounting for effects of said substantially constant residual spectra; and
(g) using said calibration parameters to determine concentration of an analyte of interest in the sample of biological fluid of the individual.
By use of one or more of these mathematical techniques, a calibration model can be derived. The calibration model and constants associated with the calibration model can be used to calculate the concentration of an analyte of interest in a biological sample.
In another aspect, the invention provides a method for measuring the refractive index of a sample of biological fluid while making spectroscopic measurements substantially simultaneously. The refractive index measurement provides the equivalent to a measurement of specific gravity, because both measurements are affected by the amount of solute in a solution. In this invention, however, the beam of light for measuring the refractive index is not co-linear with the beam of light for spectroscopic measurements. Further, pH electrodes can be used to obtain accurate pH values of a sample of biological fluid. An ion selective electrode can be used to provide nitrite values of a sample of biological fluid when nitrites are present at low concentration, while infrared spectroscopy can be used to provide nitrite values of a sample of biological fluid when nitrites are present at higher concentration.
If the spectroscopic measurements previously mentioned are combined with a cell counting method, such as flow cytometry, a fully integrated, rapid system for determining at least one parameter of at least one analyte of interest in a biological fluid as well as at least one parameter of at least one particulate material in a sample of biological fluid can be constructed. Such a system can provide enhanced automation of systems that are now only partially automated.
In order to make it possible to carry out the foregoing methods in an optimal manner, systems utilizing several novel components have been developed. To aid in enhancing measurements of refractive index, it has been found that a position-sensitive detector is preferred. Such a detector is commercially available. An arrangement for aligning the light source with the sample and the position-sensitive detector has been designed. To aid in enhancing the speed and convenience of carrying out spectroscopic measurements and refractive index measurements, a sample cell assembly having a unique geometry has been designed. In addition, in some cases, it is desirable to employ assays that employ reagents to enhance the accuracy of the reagentless system described herein. For this purpose a system that integrates the reagentless system of this invention with a reagent-using device has been developed. The integration of a reagent-using system with the reagentless system of this invention makes it possible to carry out determinations on analytes of interest that exhibit little or no spectral signature.
In a preferred embodiment of this invention, the system described herein can be used to measure creatinine, pH, and refractive index to check for adulteration of urine in a drugs-of-abuse testing environment. For spectroscopic measurements, it is preferred to employ a spectrometer, which measures the spectra of analytes of interest in a sample of biological fluid. In another preferred embodiment of this invention, the spectrometer previously mentioned can be replaced by a filter photometer unit, which involves utilization of appropriate filters to provide absorbance values at selected wavelength regions of a spectrum of interest. Regardless of which type of instrument is used to determine the spectrum, the preferred embodiments of this invention include the following components:
(1) spectrometer or infrared filter photometer unit to measure the concentration of creatinine in a sample of urine, whereby sample dilution brought about by ingestion of water or by direct dilution with other materials can be assessed;
(2) pH electrodes to assess the suitability of the sample for chemistry assays;
(3) refractometer to measure the level of dissolved solids.
Such a system may be expanded to include measurement of other adulterants, such as glutaraldehyde and nitrites. Measurement of adulterants can be simplified by selection of appropriate filters in an infrared filter photometer.
An embodiment involving a hand-held or easily portable system that can serve the workplace testing area or insurance physicals area by allowing an immediate assessment of the integrity of a urine sample collected in a remote location is also contemplated. The system may include the following components:
(1) laser diode or light emitting diode to measure the concentration of creatinine and other adulterants in a sample of urine, whereby the creatinine value obtained can be used to assess dilution of sample caused by ingestion of water or by direct dilution with water, while positive detection of other adulterants, such as glutaraldehyde or nitrites, can be used to identify urine samples spiked with such adulterants,
(2) pH electrodes to assess the suitability of the sample for chemistry assays,
(3) refractometer to measure the level of dissolved solids,
(4) temperature sensor to determine if the sample is at a physiologically significant temperature or whether a false sample has been substituted.
Concentrations of components in a sample of urine are variable depending on the state of hydration of the individual. By calculating the ratio of the concentration an analyte of interest in a urine sample (e.g., ketones) to the concentration of creatinine, measurement variability can be reduced or eliminated.
This invention provides several advantages over urinalysis systems currently in use. One of the problems for bilirubin determinations by means of test strips is caused by the stain of the reaction pad by urine, the color of which is too close to the color generated by the chemical reaction for bilirubin determination. This false positive situation is of such concern that some laboratories routinely run confirmatory tests. Because spectroscopic methods involve multiple wavelength differentiation, and do not generate a colored compound by chemical reaction, they do not suffer from the interference caused by the native color of urine.
If integrated into an automatic analyzer system or if interfaced with the ADx systems (an automated drug of abuse assay instrument by Abbott Laboratories), the reagentless system of this invention can provide a drug/creatinine ratio. The ratio can be used as a means to correct for sample dilution, and may represent a new standard in drugs of abuse testing.
The reagentless system of this invention provides improved performance, rapid throughput, elimination of reagents, and increased convenience for the user. The reagentless system of this invention allows substantial removal of base-line drift in spectroscopic measurements. The reagentless system of this invention allows determination of the concentrations of several analytes simultaneously in the presence of interfering signals in spectroscopic measurements.